Problem was, the World War II hand grenade brought in by an oblivious Hunter Christian School student – who thought it was a harmless money box – also had the potential to cause carnage.

Bomb experts confirmed that, although the detonators and pin had been taken from the grenade, explosives remained inside and could have easily become active if it was dropped – with devastating consequences.

The Mayfield campus’s 450 students and staff were immediately evacuated, with nearly 400 going home, after the 11-year-old girl had shown off her possession to a teacher before the start of school.

The grenade was taken to principal Boyd Allen’s office, and it remained on his desk for nearly three hours before RAAF experts removed it in a bomb-proof box.

It is understood the girl’s family was given the grenade by a neighbour, who told them it had belonged to an elderly relative, who had made it inert and used it as a money box.

For more than a week it stayed with the year 5 student’s family – until she decided to bring it to school for show and tell.

‘‘They are very embarrassed by the fact that this has been the response.’’ Newcastle duty officer Inspector Gerard Lawson said.

‘‘It was brought for show and tell – quite innocently as I understand it – but they appreciate now the great potential risks that they placed other people under.’’

Mr Allen said the student was not in trouble.

‘‘She’s bewildered, embarrassed,’’ he said.

Inspector Lawson said the school had acted appropriately in evacuating everyone immediately to a nearby club.

The school and a surrounding street remained in lockdown until the bomb experts arrived and took the grenade away for testing.

‘‘There is no doubt that it did pose a potential threat and the actions that we have had today are appropriate in the circumstances,’’ Inspector Lawson said.

‘‘It is timely to remind people that if you do come across anything suspicious, particularly munitions, that you alert police straight away ... ’’.